While a wide variety of machines for automatically fastening both large and small assemblies of parts together have been proposed by the prior art, for various reasons, such machines have proven to be unsuitable for use in many environments, particularly environments wherein the resultant subassembly is a major subassembly. As a result, many major subassemblies are, essentially, produced by hand, i.e., manually. For example, major aircraft subassemblies, such as wing spars for commercial air transports (which have lengths falling in the 50-100 foot range), are currently produced by skilled personnel with the aid of complex assembly tools. First, the component parts are manually positioned in the assembly tool. (The assembly tool is designed so that the parts are correctly positioned.) Next, drill plates, used to locate fastener holes, are mounted on the tool and/or the assembled parts. The fastener holes are then drilled, using manually operated equipment. The parts are next disassembled, cleaned, deburred, sealed and reassembled. Fasteners are then installed using manually operated riveting equipment. This assembly method has not basically changed since World War II, when large aircraft were first designed and produced.
Obviously, the foregoing method of assembling major aircraft assemblies has a number of disadvantages. One obvious disadvantage is that the parts must be assembled for drilling, then disassembled for cleaning and deburring, and finally reassembled for riveting, all of which is manually time consuming and, therefore, expensive.
Another major disadvantage of the foregoing assembly method is the high cost of producing and maintaining the assembly tooling. In this regard, it has been determined that the tooling used to build one spar of one wing of a modern commercial jet aircraft required approximately 45,000 man hours to design and fabricate. Maintenance of this tooling and modifying the tooling to accommodate model changes and customer variables required approximately 21,000 man hours over an eight-year period of time.
Because of the extremely high initial costs associated with producing major subassembly tooling, and because of the high costs of maintaining, modifying and using such tooling, various attempts have been made to automate at least the riveting of major subassemblies. However, at best, prior art machines have provided very limited solutions to the problem. In one system, subassemblies are first completely preassembled and entirely manually tack fastened together. Thereafter, fastener locations are established either manually by alignment to marks on the parts of the subassembly or by a rudimentary system of numerical control, which spaces fasteners between tack locations. In both instances, fastener positions are imprecise at best.
Furthermore, many prior art riveting machines move the subassembly, rather than the riveting mechanism. While such machines are useable when the subassembly is small, as the size of the subassemblies increase they become increasingly less useful because, due to inertia, large subassemblies cannot be rapidly moved from position to position. Those prior art machines that move the riveting mechanism, rather than the subassemblies, also have disadvantages. Specifically, in most such machines the riveting mechanism is massive and, therefore, slow moving. Not only are the riveting mechanisms slow moving because they are massive, they are also difficult to position.
Another difficulty with many prior art automated riveting machines is their inability to rivet (fasten) all of the parts of a major subassembly together in a minimal number of passes, regardless of the composite thickness of the parts at particular riveting points. This limitation occurs because of the inability of such machines to select a rivet of suitable length based on the composite thickness of the parts. As a result, all the rivets of a particular length must be inserted and upset at one time, followed by the installation of rivets of a different length, etc., until all of the rivets have been inserted and upset. Obviously, this approach requires that the machine pass over the surface of the part several times during an entire assembly operation, which is slow and, therefore, undesirable.
Therefore, it is an object of this invention to provide a new and improved method and apparatus for the automated assembly of major subassemblies.
It is also an object of this invention to provide a method and apparatus for the automated assembly of major subassemblies that provides for the rapid, easy and precise positioning of parts to be riveted together.
It is another object of this invention to provide an automated assembly machine for major subassemblies that quickly and rapidly performs all of the steps necessary to fasten the parts of a subassembly together at predetermined points prior to being indexed to the next fastener location.
It is a still further object of this invention to provide a new and improved automated fastening machine for major subassemblies wherein the major subassembly remains stationary while a mechanism rapidly and quickly performs all of the steps necessary to permanently fasten tacked together parts of the subassembly at different locations during a pass over the surface of the subassembly.